A dual flow turbomachine 10 for aeronautic propulsion is represented schematically in FIG. 1. It includes a fan 11 delivering a flow of air, a central portion of which, called primary flow PF, is injected into a compressor 12 which supplies a turbine driving the fan 11.
The peripheral portion, called secondary flow SF, of the flow of air is for its part ejected to the atmosphere to provide a portion of the thrust of the turbomachine 10, after having passed through a crown of fixed blades arranged downstream of the fan 11. This crown, called guide vane 14 (also known by the acronym OGV for Outlet Guide Vane) makes it possible to straighten out the flow of air at the outlet of the fan 11 while limiting losses to the maximum.
FIG. 2a schematically illustrates a blade 20 of a guide vane 14 comprising notably a body 30 and a root 21, whereas FIG. 2b is an enlargement of the root 21 of said blade 20 along a sectional plane A-A. The blades of the guide vane 14 are intended to be fixed on a hub 15. To this end, the root 21 of the blade 20 comprises two attachment openings 22 situated on either side of the body 30, making it possible to receive tightening means for mechanically linking the blade 20 to the hub 15. An attachment opening 22 in which a tightening means 23 is positioned is represented in FIG. 3.
Each attachment opening 22 comprises:                a bottom cylindrical portion 22a emerging at the level of a bottom surface 25 of the root 21 of the blade 20, adapted for the passage of a rod 24 of the tightening means 23,        a top cylindrical portion 22b emerging at the level of a top surface 26 of the root 21, adapted for the passage of a head 27 of the tightening means 23,        a shoulder 28 between the top portion 22b and the bottom portion 22a, such that the top portion 22b has a diameter Ds greater than the diameter Di of the bottom portion 22a.         
Moreover, a ring or cup 29 is intended to be positioned in the top portion 22b between the head 27 of the tightening means 23 and the shoulder 28, in the manner represented in FIG. 3. The cup 29 makes it possible to avoid matting or marking the shoulder 28 by the tightening means 23.
Yet, corrosion has been observed at the level of the attachment openings 22, which is explained by the presence of stagnant water in the top portions 22b of said attachment openings 22.
A first solution to this problem consists in re-forming the attachment openings, then potentially putting in place sockets in said attachment openings. However, once these repairs have been made, water can again stagnate in the top portions of the attachment openings and thus again cause corrosion of the attachment openings. In addition, the successive repairs end up in weakening the blade root, which impacts its lifetime.
A second solution consists in filling the top portions of the attachment openings (once the blade is in position on the hub) by a silicone based compound known by the acronym RTV “Room Temperature Vulcanizing” silicone in order to block up said attachment openings. Yet the use of this silicone based compound necessitates a long drying time and consequently causes an increase in the duration of mounting operations. The use of silicone for filling the attachment openings also increases the dismantling time, notably during maintenance operations because it is necessary to remove the compound and to clean the attachment openings before re-mounting.
A third solution is described in the patent application FR no 1454953. According to this third solution, and with reference to FIGS. 4a and 4b, seals 31 are used for filling the top portions 22b of the attachment openings 22 after mounting the blades 20 of a guide vane 14 on the hub 15. A seal 31 comprises a plug 32 and a suitable cup 35. The head of the tightening means is intended to be placed in the cup 35 and to be covered by the plug 32. Furthermore, the cup 35 is intended to be held fixed in the attachment opening 22 through assembly pins 36. A port 34 made on a side wall of the cup 35 makes it possible to guide the plug 32 by fitting together and sliding of a projecting portion 33 of the plug 32 into the port 34. This male-female system makes it possible to assure the correct positioning of the plug 32 in the attachment opening 22.
Such a seal has however drawbacks:                it is necessary to modify the cups normally used, by forming ports in said cups, and by equipping them with assembly pins,        it is necessary to carry out two piercing at the level of the bottom portion of the attachment opening, so as to maintain the cup in the top portion of the attachment opening through assembly pins,        the contact surface between the plug and the external diameter of the attachment opening is small, which enables water to infiltrate around the plug and may cause a disengagement of the plug during the operation of the turbomachine.        